Airway traffic control system



l Ch l, 1949- s. N. wlGH'r Erm.

AIRWAY TRAFFIC CNTROL SYSTEM Filed Aug. 9, 1944 3 Sheets-Sheet 2 fha/)-Gltorncg S. N. WIGHT ET AL.

AIRWAY TRAFFIC CONTROL SYSTEM s sheets-sheet s Filed Aug. 9

Ten ATTORNEY Patented Mar. l, 1949l AIRWAY TRAFFIC CONTROL SYSTEMSedgwick N. Wight and Oscar S. Field, Rochester,

N. Y., assignors to General Railway Signal Company, Rochester, N. Y.

Application August 9, 1944, Serial No. 548,660

A Claims. (Cl. 343-108) The present invention relates to combined blindflying course indicating means and blind landing apparatus andcontemplates employing radio or other wave energy responsive scanningapparatus for scanning radio radiators in the eld of view in advance ofan airplane to produce a visible replica on a screen reproducingpictorially such field of view in advance oi the airplane. The presentinvention contemplates employment oi apparatus such as disclosed in theprior application of Field, Wight and Saint. Ser. No. 517,814, filedJanuary 11, 1944, and in the application of Dicke, Ser. No. 532,181,illed April 25, 1944, now Patent No. 2,439,846, dated April 20, 1948.

Although under most weather conditions it is unnecessary to invoke theuse of special apparatus enabling a pilot to operate his airplane whollyby indications within the cab, such apparatus should be available inView of the sudden change in weather conditions that may take place, orin view of the fact that high speed airplanes may fly from fair weatherinto cloudy and fog prevailing localities. One of the short-comings ofblind flying apparatus such as is now employed is due to the inaccuracyof the information available from such blind yng instrumentalities andone of the objects oi the present invention is to make available moreaccurate information to the pilot as to the approach of his airplane tothe landing strip irrespective of visibility and weather conditions.

Another object f the present invention resides in the provision ofapparatus which will lend itself to both blind course ying andblindlanding operation even though not all of the apparatus involved isnecessarily used to perform each of these functions separately.

Another object of the present invention resides in the provision ofsuitable radio radiators or other wave energy emitting radiators foroutlining ei/ther the course of travel or glide paths, of angles ofdeclination, which the pilot may follow, in cruising and to make hislanding, very precisely.

Another object of the present invention resides in the provision of bothvertical and horizontal lines on the screen of a cathode ray tube orkinescope with respect to which the replicas of the various wave orradio radiators may be aligned or arranged to obtain very preciseinformation of the airplanes location either during level ight or duringdeviations from such ight as may be required in the maneuvering of theairplane when making a landing.

' In accordance with another object of the present invention it isproposed in at least one form of the invention to employ suitablestabilizing means so that the replica on the screen of the cathode raytube defines the location of the airplane with respect to ground locatedradiators rather than its particular oriented position in its ilight isavailable by interpretation of the replicas on the screen with respectto the lines thereon.

Another object of the present invention resides in employment of motivepower means to determine the position assumed by suitable scanningapparatus with respect to the airplane or with respect to suitablegyroscopically controlled control means and in accordance with thisobject of the invention it is proposed to provide manual control wherebythe pilot may determine whether the motive power means shall positionthe scanning apparatus, so as to have a definite relationship with theairplane itself or a denlte relationship with the axis of rotation oi'the gyroscope.

Other objects, purposes and characteristic ieatures of the presentinvention will in part be pointed out in the specication hereinafter andwill in part be obvious from the accompanying drawings, in which:

Fig. 1 shows radio radiators arranged With respect to a landing strip inan airfield which is suitable when the invention is practiced by eitherthe employment of the stabilizing apparatus or by its omission underconditions of descending 0in a glide path having only one angle ofdeclinat on;

Fig. 2 illustrates the screen of the cathode ray tube employed withreplicas of the radio radiators illustrated in Figs. 1 or 3 inrelationship to linesv appearing on the 4screen to give the pilotprecise information as to his landing operation insofar as thehorizontal lines are concerned and to indicate the course insofar as oneof the verti-a cal lines is concerned.

Fig. 3 is similar to Fig. 1 but illustrates a modiiled form of airfieldemploying two additional radio radiators which enable a pilot to descendat a steep angie of declination followed by descent at a shallow angleof declination, or he may descend at either one of these angles ofdeclination;

Fig. 3A illustrates a side view of the airfield shown in Fig. 3 with acompound glide path starting out at one angle of declination andfinishing at another and smaller angle of declination;

Fig. 4 illustrates the screen together with replicas of radio radiatorsthereon as a result of making a two slope landing when using thegyroscopic stabilizer;

Figs. 5, 5A and 5C illustrate the airplane carried apparatus of thepresent invention certain portions of which may be omitted in practisingGround Located 1 structure.-Two forms of ground located structures havebeen shown in Figs. l and 3 insofar as blind landing is concerned andthe ground located structure for an air route consists of a plurality ofradio or wave energy radiators located along an air route as moreclearly disclosed in the prior application of Field et al., Ser. No.517,814, above referred to and as conventionally illustrated in Fig. 7of the drawings which shows the three radiators, P, Q, and R of aneastbound route.

Referring to Fig. 1 wherein there has been illustrated a landing stripLS to the rear of the entrance end of which is located an entranceradiator E and at the exit end of which is located an exit radiator Xfor radiating suitable wave energy to be detected by the apparatus onthe airplane. These radiators aid the pilot in aligning his aircraft tothe landing strip LS. A pair of landing radiators J and K is provided,one radiator being located on each side of the landing strip LS and ashort distance beyond the entrance end of this landing strip. Theseradio radiators E, X, J and K are preferably constructed directional soas to emit their radiating energy in a spreading beam substantially asillustrated by dotted lines in Fig. 1.

The airfield landing strip illustrated in Figs. 3 and 3A o1' thedrawings is substantially identical to the one illustrated in Fig. l anddiffers therefrom by having an additional pair of radio radiators M andN similarly located on opposite sides of the landing strip LS but at apoint slightly farther from the entrance end than are radiators J and Kbut still far enough from the exit end to allow an airplane to bebrought to a full stop before reaching the end of the landing strip.

Fig. 3A illustrates in side elevation a compound glide path the firstportion of which is at a steep descending slope conveniently designatedGLI and which may have a 3 slope whereas the second portion of the glidepath is at a much shallower slope of say 11/2" and convenientlydesignated GL2. Under the heading of Operation it will be pointed outhow the pilot is informed as to his progress of his airplane down thiscompound glide path illustrated in Fig. 3A of the drawings. o

Airplane carried structure-In Fig. 5 of the drawings has beenillustrated conventionally the airplane carried apparatus of oneembodiment of the invention which may be used in practicing theinvention in several ways.

Referring to Fig. 5 a portion of an airplane AP has been illustrated thelower portion of the nose of which is closed by a suitable preferablytransparent cover I0 which allows the free passage of radio or otherwave energy which is to be detected by the scanning device SA which willfor convenience be called a scanning antenna. To the body of theairplane AP is secured a bracket I I, as by rivets I2, in which ispivotally supported as by a shaft I3 pinned or otherwise secured to aunitary bearing block I I and gear sector I5. This bearing block I4 hasa bearing opening provided therein substantially at right angles to theshaft I3, in which opening is pivotally supported a second shaft IBwhich shaft has fastened thereto, at the forward end thereof, thescanning antenna support 20 and at the rear end thereof a gyroscopehousing I9. In other words. the gyroscope housing I9 and the scanningantenna support 2li are rigidly supported by the same normallystationary shaft I6 as a result of which if 'the shaft I8 is adjusted toa different position in bearing block Il both the antenna supportingbracket 20 and the gyroscope housing I9 will be rotated together and ifthis shaft I6 is swung about the axis of shaft I3 both of these elementsI9 and 20 will be swung about the axis of shaft I3 in the same manner.

1n order to operate these two structures I9 and 2li into any particularoriented position the shaft I6 may be rotated through the medium of themotor MI, pinion 22 and gear 23, whereas this shaft I8 may be swungabout the axis of pin I3 through the medium of gear sector I'5 operatedby the motor M2 through the medium of its pinion 24. These motors MI andM2 are preferably alternating current motors of the split phasecondenser type and'illustrated conventionally in Fig. 5B of thedrawings. From Fig. 5B of the drawings it is readily seen that whenalternating current is connected across terminals I and 2 of the motor,the winding A will carry lagging current by reason of the induction ofthe winding A, whereas the winding B will be 'supplied with leadingcurrent due to the capacitance of condenser C, and similarly ifalternating current energy is connected across terminals 2 and 3 therelationships of leading and lagging currents will be reversed and themotor will operate in the opposite direction. The pinion 22 is providedwith a crank 25 and the pinion 24 is provided with a crank 28. Thesecranks 25 and 26 are employed when the invention is practiced bytheomission of the gyroscope hereinafter described, in which event thesepinions 22 and 2l may be rotated by hand if desired.

The supporting bracket 20 supports a scanning antenna such as disclosedin either of the two applications referred to above and -as more fullyshown in Fig. 8 of the drawings. 'I'he conventional scanning antenna SAshown supported by the support 20 of the type disclosed in the priorapplication of Field et al., Ser. No. 517.814, but the invention is notlimited to the use of this specific form of scanning antenna. Asillustrated this scanning antenna SA includes outwardly extending armsSla and l Ib extending from a shaft 30 pivoted in a fork 32 terminatingin a shaft 20 shafts 29 and 30. These generators VG vand HG supplyvoltages to the sweep plates of the cathode ray tube KN.

In the particular embodiment of the invention illustrated in Fig. 8,although other forms of scanning apparatus may. of course. be used. thescanning apparatus includes a main shaft 29 which is positionedhorizontally with respect to the airplane and at right angles to thedirection of movement of such airplane. Inother words, the

scanning apparatus illustrated is so oriented with respect to thedirection of airplane flight as indicated by its oriented relation tothe arrow |29 (see Fig. 8) that high speed horizontal and low speedvertical scanning is accomplished.

The shaft 29 is supported by fixed bearings 20a. One end of this shaft29 is driven by a motor SMI and the other end of this shaft isbifurcated to form a fork 32 which fork constitutes rotating bearingsfor a second shaft 39 having its axis substantially at right angles tothe shaft 29 and supporting two directional radio receiving antennas Aland A2. This shaft 30 is driven by another motor SM2 which receives itsenergy through wires a and b and slip rings |3| and |32 on shaft 29. Tothe shaft 30 is pinned a U-shaped member Sia-Sib as by a pin |36 whichsupports the directional radio antennas Ai and A2 in such a manner thatthe axis of these radio antennas A! and A2 are substantially at rightangles to the shaft 30 and displaced about the shaft at an angle of 180degrees. These antennas AI and A2 comf prise parabolic metallicreflectors which have an antenna element |35 located in the focusthereof. These antenna elements |35 are connected to two segments |39and |31 of a commutator. This commutator is engaged by brushes |38 or|38a in such manner that only the forwardly directed antenna A! or A2will be electrically connected to the proper contact brush |38 or ia.These contact brushes |38 and |3Ba are in turn connected to the inputside of the amplifier-detector unit AF through the medium of Wires c andd and commutator |39|39a. It should be observed that if We assume theshaft 30 to be stationary in the fork 32 that the connections to theantennas AI and A2 must be commutated with.respect to rotation of shaft29 and it isfor this reason that commutator |39|3Sa is provided.

From this construction it is readily seen that only the focused antennadisposed to the front of the airplane will be electrically connected tonamely, has rotated to a position where the shaft 80 is horizontal thedirectional antenna A| will come out of view of the field of visionahead of the airplane and'the directional antenna A2 will enter such afield so that another 32 lines may be scanned by the antenna A2. .Thismakes a total of 64 lines of scanning per revolution of the shaft 29.Also, as the antenna A| passes out of the eld the amplifier-detector,and it is further readily seen that upon high speed rotation of theshaft 3B the focal lines of the focused antennas AI and A2 will describesubstantially horizontal lines one above another the spacing betweenthese lines depending upon the ratio of speeds of rotation of the shafts29 and 30. In otherwords, if the shaft 39 rotates 16 times while theshaft 29 rotates a half-revolution, 52 horizontal lines will be scannedover'the field for each frame of observaton or each half-revolution ofthe shaft 29. It will also readily be seen that when the shaft 29 hasbeen rotated 90 from the position shown,

of vision the brushes |39 and |3811 pole change on segments |36 and |81.In this connection it should be understood that if it is desired to scanonly below the horizon and if it is desired to only scan a horizontaldistance of 45 to the right oi the course of the plane and 45 to theleitvof the course of the plane, namely, if it is desired to scan anarea by 90 two more directional antennas placed at right angles to thetwo illustrated would be employed in which event four pole generatorsinstead of two pole generators, to described hereinafter, would berequired to be employed. In this case the commutator ISB-|31 would be.required to be a four segment commutator.

The shaft 29 is provided with a two-pole generator VG and the shaft 30is provided with a.

two-pole generator HG. Since these generators are identical, like partswill be designated by like lreference characters having distinctiveexponents and only one of-these generators will be described in detail.Referring to the generator HG associated with the high speed shaft 3i)this generator comprises a permanent magnet field magnet PM2 supportedon one leg of the fork 32 'by brackets |622, between the north pole Nand the south pole S of which is supported a soft iron laminatedarmature ARl secured to the shaft 3@ as by a pin |642. On this armatureAR:i is provided a winding W2 which has one end electrically connectedto the commutator segment |602 and has its other end electricallyconnected to the commutator segment IM?. Stationary brushes |4352 and|962 displaced about the shaft 30 engage the commutator N92-iti. 'Ihesebrushes are so oriented with respect to the eld magnet PM2 thatcommutation from one segment to another, or pole changing of the wires eand f leading from the armature winding W2 and connected to slip ringsitil and |98 takes place when there is substantially zero flux in thearmature AR". In other words, these generators HG and VG do not deliverdirect current as is usually the case of generators of similarconstruction because they commutate the current at the maximum voltagevalue rather than at zero voltage value as is customarily done. Thevoltage delivered at the brushes is therefore substantially of saw-toothform.

Since the commutator it-i3? and the commutator IML-IN2 perform theircommutating function at the same time it will be seen that the voltagedelivered by the generator HG is of maximum plus value when a newfocused antenna enters the field and that this voltage is of maximumminus value when such focused antennaleaves the eld which is beingscanned. The voltages delivered by these generators HG and VG are usedto deflect the electron beam of the cathode-ray tube KN all in a manneras hereinafter more fully described. l 4

The cathode-ray tube KN, commercially known as a kinescope andillustrated in the upper left part of Fig. 5 and in Fig. 8 ofthedrawings is of well known construction and is employed to visuallyindicate on a fluorescent screen the pictorial location of one or moreof the ground located radio transmitting antennas. Cathoderay tubes oi'this construction are well known in the art for which reason thekinescope KN has been illustrated rather conventionally.. Thiskinescop'e comprises a fluorescent screen S, also shown in Figs. 2 and4, over which an electron beam is adapted to sweep in a manner to Vhedescribed hereinafter. This electron beam has been shown at twodifferent positions by a dotted line and by a dot and dash line. Theelectron beam is located in the position as shown by the dotted linewhen the sweep voltage delivered by the generator HG is of maximum plusvalue and the sweep voltage delivered by the generator VG is also ofmaximum plus value. Under the condition of zero sweep voltagestheelectron beam of Fig. 8 will assume a neutral position as shown by thedot and dash line. This swing of the electron beam is accomplished byhorizontally located sweep plates |59 and |5| connected to the highspeed generator HG and by the vertically located sweep plates |52 and|53 connected to the brushes of the low speed generator VG. As is weilknown Iby those skilled in the art the electrons are emitted by theheater or cathode |55 which is heated by a filament |56 as through themedium of a battery |63 The electrons emitted by the cathode |55 may becontrolled by a grid or controlling element |51 and may be brought to asharp focus by the focusing or anode structure |56. A second anode |59is provided on the inner surface of the tapered portion of thecathode-ray tube to accelerate the electrons after the grid or controlelement |51 has once allowed these electrons to be emitted. Asillustrated the focusing structure or rst anode |58 vhas a potentialapplied thereto through the medium of the battery |69 and apotentiometer |6|, so that by adjusting the slide contact |62 of thispotentiometer the electron beam may be focused so as to concentrate theelectrons into as narrow a beam as desired. It should be understood thatthe cathode |55, the grid |51 and the anode |56 constitute the so-calledelectron gun whereas the cathode |59 is the optical system for focusingthe electron beam into a narrow stream. The screen S may also be calledthe target.

When a focused receiver A| or A2 receives a momentary radio or otherwave energy signal, this reception being momentary on account of thehigh speed rotation of these antennae AI and A2 in two different planes,current flows over the wire 33 and through amplifier and detector AF tothe grid of the cathode-ray tube KN.

Within the gyroscope housing i9 is pivotally supported a shaft -35 whichterminates into a U- shaped fork 36, only one leg of which is visible inFig. of the drawings. This fork 36 is provided with bearing pins 31extending inwardly from the two legs of the fork and comprise pivots forpivotally supporting the gyroscope frame 34. Within this gyroscope frame34 'is pivotally supported as by a shaft 39 a ily wheel or gyro 38 of agyro artificial horizon indicator such as, for instance, disclosed onpages 73 and 85 of Civil Pilot Training Manual, furnished by the U. S.Department of Commerce, and dated September, 1941, or as disclo.'.ed inthe A. I. E. E. Technical Paper 44-70, dated December, 1943, disclosingan electrically operated gyro horizon indicator.

This fly wheel or gyro 36 may be either pneumatically driven as are thegyros disclosed in the above referred to Pilot Training Manual or it maybe electrically driven by a suitable high fre- 8 quency alternatingcurrent motor as is true of the apparatus described in the abovereferred to A.v I. E. E. Technical Paper, and whether it isvpneumatically or electrically driven the supply of power thereto may bemanually cut on'or oi! as desired. this manual control having forconvenience beenomitt'ed from the drawings.

To one leg of the fork 36 is secured, but insulated therefrom, a movablespring contact finger 46 which is arranged between two relativelystationary contacts 4| and 42 supported on the gyroscope frame 34. It isthus seen that if the fork 36 moves from its neutral position in onedirection or the other about the pivot 31, the gyro frame 34 being attimes held stubbornly in its oriented position by the gyro 36, thecontact 40 will engage one or the other of contact 4| orl contact 42 andif the fork 36 is moved` in the opposite direction about the pivot 31the opposite contact 4| or 42 is engaged by contact 46. Similarly, aspring contact arm 44 is supported by the shaft 35 and extends radiallytherefrom and between relatively fixed contacts 45 and 46 supported by,but insulated from, housing I9. Therefore, spring contact 44 may engageone or the other of contacts 45 or 46 depending on the temporaryrotation of gyro housing I9 about shaft 35'. From this structure it isreadily seen that if the shaft 35 is turned in one direction from itsneutral position in housing i9 it will engage the contact 45 and if itis turned in another direction from such'neutral position it will engagethe contact 46. These contacts 40, 4|, 42, 44, 45 and 46 are used tocontrol the motors MI and M2 when the antenna supporting bracket 20 isto be positioned to conform with the position then assumed by the axisof rotas tion of the gyro 38.

Two additional sets of contacts 5|), 5|, 52, 54, 55 and 56 are providedto similarly control these motors MI and M2 when the antenna supportingblock 26 is to be positioned and oriented with respect to the body ofthe airplane itself. In other words, the contacts 50, 5| and 52 performfunctions corresponding to the functions performed by contacts 40, 4|and- 42 and the contacts 54, 55 and 56 perform functions comparable withthe functions performed by the contacts 44, 45` and 46. These functionswill be more specifically pointed out in the operation of the systemhereinafter.

An end view of the contacts 44, 45 and 46 and the shaft 35 on which thecontact 44 is supported has been illustrated in Fig. 5A of the drawings.Similarly, the contacts 54, 55 and 56 and the manner in which contact54' is secured to shaft I6 is indicated in Fig. 5C of the drawings. Asreadily seen from the drawings, the motor MI is controlled by either thecontacts 44, 45 and 46 or the contacts 54, 55 and 56 depending upon theposition assumed lby the two pole double-throw switch 48, whereas themotor M2 is controlled by either the contacts 49, 4|, 42 or by thecontacts 5|), 5|, 52 depending upon the active position assumed by thedouble-pole double-throw switch 4'9.

, the transformer Tr and this alternating current may also be used forspinning directional -antennae AI and A2 about two axes at right anglesto each other at comparatively high speeds and which may also be use forpropelling the gyro 38 at very high speed.

Modern airplanes are provided with suitable inthe pilot in maneuveringhis airplane. Only those instruments that are essential in practicingthe present invention have been illustrated conventionally in thedrawings and they include an altimeter AL for convenience shownsupported from the airplaneAP through the medium of a bracket 58 and twoball-type inclinometers 59 and 60 preferably supported in a manner tomove re1- atively to the airplane in exactly the same way as the antennasupporting -block 20 is positioned relative to the airplane. As shownthe inclinometer S is supported on the rear face of the gyroscope casingI9 to indicate the rocked position of support 20 whereas theinclinometer 60 is supported on a side wall of this casing is toindicate the extent of nosing of this support. These inclinometers 5Sand 60 each comprise a slightly bent round tube of glass the ends ofwhich are sealed and in which there is contained a metal ball preferablyof a diameter slightly smaller than the inside diameter of the glasstube, this tube then being filled with a suitable transparent liquidsuch as clear oil. These in.- clinometers are merely dampened levels andindicate to what extent the support therefor has been moved from aperfectly level position in that if one end of this tube is higher thanthe other the ball will roll toward the lower end to an extent dependingon the tilted position assumed by the tube, the oil being employed todampen the movement of the ball so that it will not move aboutunnecessarily. It is thus seen that the inclinometer ii will indicatethe extent of banking oi the scanning antenna bracket 20 whereas theinclinometer t@ will indicate the extent of nosing up or down ofthisscanning antenna supporting bracket 2t and the scanning antenna mountedthereon.

OPERATION Operation gyra-stabilizer During iying over a route deiined bysuccessive ground located radio radiators irrespective of' whether thereis good or poor visibility and irrespective of whether radio energy orsome other fog penetrating wave energy is used the appara tus of thepresent invention will be useful in more accurately flying over suchroute. This is especially true because the route over which the pilotproposes to fly may not have sumcient markers thereon visible to the eyeto adequately aid the pilot during clear weather flying.

In any event, and in accordance with the present invention, when thepilot flies over a traffic route it will be necessary for him to holdhis scanning antenna so as to assume a predetermined xed relationshipwith his airplane. And this relationship is preferably such that thescanning antenna supporting bracket 20 points level and directly aheadover the route when the airplane is flying level. In order to establishsuch relationship between the antenna supporting bracket 20 and theairplane AP the two selecting switches d8 and t9 are operated to theirrighthand position. The closure of the switch t8 to its right-handposition will cause current to ow from theA left-hand terminal of thesecondary winding 66 of the transformer Tr over wires Si and 62 tocontact Se' supported by but insulated from the shaft i8. If this shafti0 is now in any other than its neutral position with respect to thebearing block it current will flow from contact 56 to either contact ator @t and their respective wires a or 5ta to in turn cause operation ofthe lmotor M I in a direction to cause the contact te flow from theleft-hand terminal of the secondary winding t3 of the transformer Trover wires @il and t5 to contact il@ which moves with segment l5.' Ifthis contact E@ does not assume its middle position current will beapplied to one or the other terminal i or il of the motor M2 throughcontact 5i and wire Sia or through contact E2 and wire 52a, to therebycause this motor MZ to operate the gear sector l5 until the contact 50again assumes its middle open position. `With the contact E@ assumingits middle position the bearing block i@ and the shaft it pivotedtherein will assume a position parallel to the plane of flight of theairplane, and with the contact 06 also assuming its middle position theshaft it assumes a nonbanking position during level flying.

Let us now assume that the pilot has completed his trip over the airroute in a manner as clearly described in the Field, Wight and Saintapplicai tion and is about to make a blind landing. 1n practicing thatform of the invention where the gyroscopic stabilizer is used for makingblind landings the pilot .will cut his gyroscopic stabilizing apparatusinto operation. To do so the operator will iirst operate suitable manualmeans such as an air valve or a switch (not shown) for supplying energyto the gyro 3d to cause it to accelerate until it reaches its full speedof about 20,000 R. P. M. While the gyro 88 is being acce1- erated, whichmay take several minutes, the pilot will make a real effort to y atconstant altitude by observing the indication from his altimeter AL, andwith a minimum of nosing either up or down or banking. This even flyingat constant altitude is not necessarily yaccompanied by the airplanebody assuming a level position due to the extent and distribution ofairplane loading. The gyroscope frame ad ispreferably weighted as by aweight W so that the axis of rotation of the gyro 30 will be perfectlyperpendicular when this gyro @t comes up to its full operating speed.The operator will have in the meantime operated both of his selectingswitches i8 and it to the l1 mined by shaft i8 is concerned and insofaras its nosing position about the axisof shaft Il is concerned. Thislevel position of the scanning l antenna supporting bracket 20 will bemaintained throughout the entire landing operation irrespective ofirregular movements of the lairplane in making a carefullyncontrolledl-anding.

It may be pointed out here that the screen S of the kinescope KN isprovided with a level plane line LP and with a vertical center line 10(Figs. 2, 4 and 5), and with the scanning antenna supporting bracket 20maintained in its level plane position any horizontally emitted radiobeam which strikes the scanning antenna Ai or A2 will cause a spot oflight to appear on the level plane line LP and if'this beam is radiatedfrom directly ahead the spot will also fall on this vertical line Toreturn the apparatus to route ying operation all that is necessary isthat the double-throw switches 48 and 49 be returned to their righthandposition and the power supply for rotating the gyro 38 be cut off. 1

If the invention is practiced by omitting the gyrosco'pic stabilizer itmay at times, due to unusual loading of the airplane, be necessary toposition the scanning antenna supportingbracket differently with respectto the airplane than the plane-axial relationship above mentioned. Inthis form of the invention the motors MI and M2 may be omitted but theirrespectivepinions 22 and 2l will be retained, these pinions in this casebeing turned by hand through the medium of cranks 25 and 28respectively. These cranks 25 and 2B will in this case be turned until aradio beam approaching in plane-flight axial line will place its imageat the point on the screen S where lines l0 and LP cross. Or thesecranks may be adjusted until both of the ball inclinometers 59 and 60assume their level position.

Operation system Blind landing omitting stabilizer.-As already pointedout above the scanning antenna stabilizer apparatus may be omitted andin this case the invention is used in a slightly different manner thanwhen this stabilizer is used. When the stabilizer is omitted it isassumed that the motors MI and M2 are also omitted and that in this casethe scanning antenna supporting bracket 20 is adjusted to a non-banked,non-nosing level position by the operation ofthe cranks 25 and 28. Forinstance, if the pilot uses the inclinometers 59 and B0 he will operatethe crank 25 until the ball in the inclinometer 59 assumes the middleposition and will then operate the crank 26 to a position where the ballin the inclinometer B0 assumes the middle position. These adjustmentsand particularly the adjustment of crank 26 is necessary 'to compensatefor different conditions of loading of the airplane. If the airplane isheavily loaded it will be required to nose slightly higher and for thisreason the crank 26 will havev to be turned slightly to the left fromits normal position. These cranks 25 and 26 may be frictionally orotherwise locked into their last operated position.

Proceeding now on the assumption that the scanning antenna supportingbracket 20 is properly adjusted and that the scanning antenna isoperated and all the circuits (see Field et al. application) leading tothe kinescope KN are closed, the operator will observe replicas of thevarious ground radio radiators ahead of the plane. If he is flying.without crabbing (pointing into a side wind) on a course such asindicated in Fig. 'I of the drawings he will have these replicas linedup on the vertical line 10 on the kinescope screen S. If he is crabbinghis airplane he will line up the replicas sidewise differently to anextent depending on the extent of crabbing.

Let us now assume that he is approaching an airneld such as shown inFig. 1 and that he contemplates landing on the landing strip LS undersevere fog conditions. As he approaches the air strip LS, ilying in adirection to approach the entrance end E i'lrst, he will line up the tworeplicas of radiators E and X on the line 1l of the kinescope screen S(see Fig. 2) and will maintain level flight so far as possible. As heapproaches closer and closer to theentranoe of the landing strip LS thereplicas 1| and ki will nnally register on the horizontal line GLI,which we may assume to constitute a declination line or glide pathdisposed at an angle of 3 with respect to the level flying field. Thisarrival. of the replicas di and Ici on the line GLI will inform thepilot that he is crossing a declination line, assumed to be a 3 line,which terminates vnear entrance end of landing strip LS. The

. pilot will now nose his airplane downward very quickly until the spotsj and k have shifted to the positions :i2 and k2 on the level flightline LP. This informs the operator that he is dying directly toward theradio radiators J and K on opposite sides of the landing strip LS. Iithe pilot continues tokeep the replicas of radiators J and K on the lineLP these replicas will gradually spread apart and when they have reachedthe vertical lines 1I and 12 respectively the wheels of his plane willtouch the landing strip near the entrance end thereof.

Had the pilot desired to make his descent rst at a large angle of say 3with respect to the horizontal as just described, followed by a glidepath of smaller declination angles, such as 11/2 with respect to thehorizontal flying neld. the flying eld would have to be provided with anadditional set of radio radiators M and N as shown in Fig. 3 of thedrawings. In this case the pilot would have returned his airplane tolevel flight, as shown by dotted line 13 (Fig. 3A) when the images 1 andk have separated a predetermined distance from the center line 10 and hewould then have maintained this level flight (line 13) until thereplicas or images of radiators M and N appear on the glide path lineGL2 (assumed to be a 11/2 declination line) on his kinescope screen.When this is observed the pilot will know that he is then crossing themore shallow glide path line of slope GL2 (see Fig. 3). He will thenagain nose his airplane downward slightly until the images m and nappear on the level line LP after which he will continue his flight downthis glide path of smaller slope until the images m and n have separatedto an extent to have reached the vertical lines 1I and 12 at which pointin his flight his airplane wheels will just touch the landing strip LS.

It has thus been pointed out that without the employment of thegyroscopic stabilizer shown in Fig. 5 and assuming that weatherconditions.

straight declining path toward such radio radiators. It has also beenpointed out that after he has gilded down a glide path of rather steepdeclination he may shift to a glide path of more shallow declination bytemporarily flying level (See dotted line 73, Fig. 3) and that he willeventually make a landing on the landing strip instantaneously withcertain visual information displayed on his kinescope screen. Understormy weather conditions the accuracy of blind landing of an airplaneis naturally diminished and for this reason the employment of thegyroscopic stabilizer disclosed in Fig. is believed a desirable adjunct.

Blind landing using stabilizer.-From the operation just considered it isobvious that the replicas on the screen reflect not only the location oithe airplane in space with respect to the radio radiators of which thesereplicas are images but also rellect the oriented position of theairplane at this point in space. it is readily seen that ii a gyroscopicstabilizer is used to stabilize the scanning antenna supporting bracket2li that under this condition most orientation changes of the airplanehave been eliminated and the images on the screen S will reflect ormanifest solely the position assumed by the airplane in spaceirrespective of its oriented position except for orientation about avertical 'ams about which the scanning antenna is not stabilized. Fromthis consideration it is of course apparent that the procedure ofmelting a blind landing when using `a gyroscopic stabilizer must ofnecessity be quite dlerent from the procedure when using the sameapparatus when no gyrcscopic stabilizer is ernn ployed.

Let us now assume that the pilot is about to malte a landing on alanding strip such as shown in Fig. 3 of the drawing except that it isemploying only a single pair oi radio radiators J and l. Durlng night ofthe airplane equipped as illustrated in Fig. 5 over an air route asillustrated in Fig. 7 the double-throw switches is and le will assumetheir right-hand position in which position the scanning antennasupporting frame all is lined up level with the airplane itself all forreasons hereinbefore, described. For reasons already pointed out thegyroscopic stabilizing apparatus must be cut into service when a blindlanding is contemplated. To make this blind landing operation the pilotwill irst set his gyro il@ into operation in a manner as described underthe heading "Operation gym-stabilizer and he will simultaneouslytherewith operate the doublethrow switches is and de to their left-handposition.

As the airplane moving in an E to X direction approaches the entranceend E on the landing strip LS in Fig. 3 of the drawings, he willcontinue level flight until the image point ii and Ici appear on thehorizontal line GLi (see Fig. 4) and if these images of radiators J andK are held on this line GLi by the pilot properly maneuvering hisairplane these images will gradually spread or separate. When theseimages have separated to an extent to reach the points d2 and k2 (Fig.d), y

it being understood that the maneuvering of the airplane just mentionedresulted in the airplane following a steep glide path GLl, which we mayassume to be a slope of say 3 declination, the airplane has reached theshallow glide path terminating at radiators M and N. That is; when theairplane in gliding down this steep glide path, as determined by theline GLI on his kinescope screen S (see also Fig. 3A), has reached d acertain point on this glide path, as mania fested by the image points 12and k2 `(We. 4) reaching the. vertical lines 'il and l2 respectively,the images of the radio radis-f tors M'and N will have reached the lineGL2 as manifested by the dots m2 and n2 in Fig. 4 of the drawings. Inother words, the replica of the four radiators J, K, l.. and M willfirst appear on the kinescope screen S in the form of a frustum of atriangle defined by image points i i, Ici, mi and nl but after theairplane approaches closer to the landing strip LS in Fig. :l thisfrustum of a triangle will have been enlarged on the screen S as ismanifested by the image points 72. k2 m2 and n2. When this point in thedescent ci the airplane tow-ard the landing strip down the steep slopeis reached the pilot will disregard the image points :l2 and k2 and willdirect his attention to the image points m2 and n2. In fact, the pilot`will maintain the images m and n on the line @Li-l, which for obviousreasons will mean that the air plane is now descending on the shallowglide path which wemay assume to have a declination oi' lt/g withrespect to the horizontal airiield. As these images m and n move aparton the line Glad (Fig. d), the pilot of course trying to keep theseimage spots m and n equal distances from the vertical line le, they willeventually reach points mil and nil. When these images in and n by theirseparating movement have reached the points oi intersection of line @L2with vertical lines li and 'i2 as manifested by' the image points ml andad the wheels of the airplane will just touch the landing strip LS andthis will occur at a predetern mined distance from a line connecting theradio radiators M and N along this landing strip l@ (Fis. t).

Under the operation `lust considered the pilot and his airplane camedown a' steep glide path until this glide path crossed a more shallowglide path and then'he followed the shallow glide path until his wheelstouched the landing strip LS. It is of course obvious that he could havemain tained his flight down the original and steeper glide path in whichevent he would have landed with respect to radiators J and l rather thanwith respect to radio radiators M and N and, on the other hand, if hedesired to make the landing entirely by following a shallow glide pathhe could have disregarded the images of radio radiators J and K andcould have merely followed the images of the radio radiators M and N andhave lined them up on line GL2 on the screen instead of iirst lining upthe images of radio radiators J and K on line GLU of the screen as abovede scribed. In other words, the apparatus illustrated in Figs. 3, i and5 enables the pilot to malte an Iaccurate landing irrespective of howmuch a bat tering wind causes the airplane to roll around in spaceeither by descending a steep glide path all the way to the airiield, bydescending along a shallow glide path all the way to the landing stripor by following the steep glide path until it crosses the shallow glidepath after which he may follow the shallow glide path until his wheelstouch the landing strip, and in each case the pilot will be definitelyand precisely informed the instant Just before his wheels touch thelanding strip.

Having thus shown and described apparatus which lends itself to flyingan airplane course deilned by a plurality of radio or other wave energyradiators located along such course 'and which also lends itself toblind landing on an airfield equipped with suitably arranged radiators.the

images of which may be definitely controlled to persoribe positions in akinescope screen, so as to make an accurate and precise landing in spiteof a he'avy fog or extreme darkness without the use of any form of lightsignalling, it should be understood that the several forms of theinvention have been illustrated as examples of apparatus that may beused to carry out the purpose of the invention and it should beunderstood that various changes, modifications and additions may be madeto the invention as required under various conditions encountered inpr-acticing the invention without departing from the spirit or scope ofthe invention except as demanded by the scope of the following claims.

What we claim is:

1. Combined blind course indicating and blind landing apparatus of thetype described comprising; the combination with airplane carried radioradiator display apparatus including a scanning antenna and acathode-ray tube including a screen upon which a plurality of groundlocated radio radiators may be simultaneously displayed in perspectivein substantially the same relationship as viewed from the airplane; ofgyroscopic stabilizing apparatus for stabilizing the scanning antennabut allowing free maneuverability of the airplane; said stabilizingapparatus including a gyroscope having its casing supported rigidly withrespect to the support for said scanning antenna and having a first setof two control devices one device manifesting movement of the gyroscopesupporting frame about one axis at right angle to the spinning axis ofsaid gyroscope andthe other device manifesting movement of said frameabout another axis at right angle to both of said first mentioned axis;motive power means controlled by said control devices for holding saidscanning antenna and said frame in its original position. a second setof control devices for controlling said motive power means about twodifferent axis to cause said scanning antenna to assume aspeciflc'relationship with respect to said carrier airplane; two groundlocated radio radiators one on each side of a landing strip on anairfield; a horizontal line on the screen of said cathode-ray tube at aheight such that if a spot characterizing a ground located radioradiator is held on said `line by the pilot by maneuvering his airplanesaid airplane will descend at an angle of a predetermined number ofdegrees declination; whereby if two spots identifying said two groundlocated radio radiators are both held on said line until said spots haveseparated a predetermined distance on said line the carrier airplanewill land on said landing strip at a point predetermined by said twoground located radio radiators; and selecting means for causing saidsecond set of control devices to control -said motive power means whenthe carrier airplane is flying over a course dened by radio radiatorsarranged in a line and for causing said first set of control devices tocontrol said motive power means when the carrier airplane is about to meke a blind landing.

2. Blind landing apparatus of the type described comprising; thecombination with airplane carried radio radiator display apparatusincluding a scanning antenna, sweep-plate voltage generating means and acathode-ray tube including a screen upon which a plurality of groundlocated radio radiators may be simultaneously displayed in perspectivein substantially the same relation to each other as viewed from theairplane; of gyroscopic stabilizing appara- 16 I ratus for stabilizingthe scanning antenna but a1- lowing free maneuverability of theairplane: said stabilizing apparatus including a gyroscope havling itscasing supported rigidly with respect to the support for said scanningantenna and having a first set of two control devices one devicemanifesting movement of the gyroscope supporting frame about one axis atright angle to the spinning axis of said gyroscope and the other devicemanifesting movement of said frame about another axis at right angle toboth of said first mentioned axes; motive power means controlled by saidcontrol devices for operating said frame back to its original condition;a second set of two control devices for controlling said motive powermeans about two diiferent axes to cause said scanning antenna to assumea specific relationship with respect to said carrier airplane; twoground located radio'radiators one on eachside of a landing strip on anairiield; a horizontal line on the screen of said cathode-ray tube at aheight such that if a spot characterizing a ground located radioradiator is held on said line by the pilot by maneuvering his airplanesaid airplane will descend at an angle of a predetermined number ofdegrees declination; whereby ii' two spots identifying said two groundlocated radio radiators are both held on said line until said spots haveseparated a predetermined distance on said line the carrier airplanewill land on said landing strip a predetermined distance to the rear ofsaid two ground located radio radiators; and Y selecting means fordetermining whether said first set or said second set of control devicesshall control said motive power means.

3. Blind landing apparatus of the type described comprising; an airplanecarried cathoderay tube including a screen; apparatus on the airplaneincluding a scanning antenna. means for swinging the electron beam inthe cathoderay tube and ilring the same, to cause a replica of groundlocated radio radiators in the field to appear on the screen insubstantially the same relationship to each other as they appear in thefield ahead of the airplane; two horizontal lines on said screen, thefirst line of which is so located that if said scanning antenna ispositioned for level flight a radio beam inclined at a predeterminedangle will manifest itself on said line and the second line so locatedon said screen that a radio beam inclined at a predetermined but smallerangle will manifest itself on such second line; gyroscopic stabilizingapparatus for stabilizing said scanning antenna to level night butallowing free maneuverability of the carrier airplane; two pairs ofradio radiators one radiator of each pair being located at equaldistances on opposite sides of a landing strip on an air field with thefirst pair located near the entrance y end of said landing strip and thesecond pair located a predetermined distance in advance thereof; wherebyif the two spots constituting the replica of said first pair of radioradiators is held on said first horizontal line by the pilotsmaneuvering of said carrier airplane until two spots constituting thereplica of the second pair of radio radiators fall on said secondhorizontal line and the airplane is then maneuvered to hold these secondtwo spots on said second line until they have separated a predetermineddistance such airplane will rst descend on a glide path havingpredetermined declination, will then descend on a glide path having asmaller angle declination and will then land on said landing strip apredetermined distance to the rear of said other 'asoaoss pair of radioradiators: and means for rendering said stabilizing apparatus ineectiveand for locking said scanning antenna on said airplane for level flightwith said airplane flying level.

4. In combination, an airplane carried support, a gyroscope, a rstcontrol means controlled in accordance with the oriented relationship ofsaid support with respect to the axis of said gyroscope, a secondcontrol means controlled in accordance with the oriented relationship ofsaid support with respect to said airplane, motive power means fordetermining the oriented position of said support with respect to saidairplane. and manually operable means to select whether said motivepower means is to be controlled by said'flrst control means or saidsecond control means.

5. In combination, an airplane carried support, a gyroscope, a firstcontrol means. including two contacts each movable between two othercontacts and controlled in accordance with the oriented relationship ofsaid support with respect to the axis of said gyroscope, a secondcontrol means including two contacts each movable between two othercontacts and controlled in accordance with the oriented relationship ofsaid support with respect to said airplane, two electric motors fordetermining the oriented position of said support with respect to saidairplane, and manually operable means for determining whether saidelectric motors are to be controlled by said rst control means or saidsecond control means.

6. In a blind landing system having two radiators transversely spacedwith reference to a landing strip, slide path defining apparatus on anaircraft comprising, a directional antenna, azimuth and elevationscanning means causing said antenna to scan the area ahead of theaircraft, means including a gyroscope for stabilizing said antenna withrespect to orientation of said aircraft about transverse andllongitudinal axes, a radio receiver having its input governed by saidantenna, a cathode-ray tube having its grid governed by the output ofsaid receiver, and sweep circuit means synchronized with said scanningmeans cooperating with the grid control of said cathode-ray tube toindicate the location of said radiators substantially as viewed inperspective from the aircraft along a particular horizontal line on thescreen of said tube whenever said aircraft is on a glide path at aparticular predetermined elevational angle from said landing strip,whereby said radiators are indicated above or below said horizontal linein accordance with said aircraft being respectively below or above saidglide path, and whereby the indications ofthe locations of saidradiators are unaffected by orientation of said aircraft abouttransverse or longtitudinal axes.

7. In a blind landing system having two radiators for. marking a landingstrip, said radiators being spaced from each other along a linetransverse to said landing strip. glide path dening apparatus onl anaircraft comprising, a directional antenna scanning mechanism on saidaircraft, a support for said antenna mechanism by which said mechanismcan be operated to a limited extent about longitudinal and transverseaxes with respect to said aircraft, a gyroscope pivotly disposed on saidsupport -to maintain a true vertical spin axis irrespective of relativeoperation of said support about said transverse and longitudinal axes.electrically operable control means responsive to a smallout-of-correlongtitudinal axes as required to correct for saidout-of-correspondence conditions, a cathode-ray tube, and meansincluding said tube and said antenna scanning mechanism for indicatingthe relative location of said radiators -on the screen of said tube inpositions with respect to a predetermined reference line on said screenabove or below said reference line in accordance with whether saidaircraft is respectively below or above a glide path at a predeterminedelevational angle extending from said landing strip, irrespective of theorientation of the aircraft about respective transverse and longitudinalaxes.

8, In a blind landing system having two pairs of transversely spacedradiators marking a landing strip, the respective pairs beinglongitudinally spaced with respect to the landing strip, glide pathdenning apparatus on an aircraft comprising, a directional antenna,azimuth and elevation scanning means causing said antenna to scan thearea in advance of the aircraft, means including a gyroscope forstabilizing said antenna with respect to orientation of said aircraftabout transverse or longitudinal axes, a radio receiver having its inputgoverned by said antenna, a cathode-ray tube, and means including theoutput of said receiver and said cathode-ray tube for indicating therelative locations of said radiators substantially as viewed inperspective from said aircraft on the screen of said tube, whereby whenone of said pair of radiators is indicated along a particular horizontalline on said screen said aircraft is on a first glide path extendingfrom said landing strip at a particular elevational angle, and wherebywhile ying said first glide path, the intersection of a second glidepath at a lesser angle is indicated by the presence of the indicationsfor the location of the other pair of radiators along anotherpredetermined horizontal line on said screen.

9. Blind landing apparatus ofthe character del scribed comprising, thecombination with aircraft carried radiator location indication apparatusincluding a receiver and a cathode-ray tube having a screen upon whichindications of the locations of radiators marking the opposite sides ofa landing strip may be displayed in perspective as viewed from the frontof the aircraft, said screen having a horizontal reference linevertically disposed thereon to correspond to a particular predeterminedelevational glide angle as viewed from the front-of the aircraft when inlevel flight, of means including a direction scanning antenna andsynchronized sweep circuits for control of said tube for indicating thelocation of said radiators respectively on said screen, and gyroscopicstabilizing apparatus in which a gyroscope has atruly vertical spin axiseffective to stabilize said antenna with respect to a true vertical axisirrespective of the maneuvering of said aircraft, whereby the replica ofthe location of said radiators on said screen along said horizontal lineis a true indication of the intersection of a glide path extending tothe landing strip at said predetermined angle, irrespective of theorientation of the aircraft about transverse or longitudinal axes, andwhereby the maintaining of the replica of the respective radiananasbeing indicated by the spacing between the replica of the respectiveradiators.

10. In a blind landing system of the character described, thecombination with radiators spaced on opposite sides oi.' a landing stripand an aircraft having a receiver responsive to said radiators, ofdirectional antenna means on said aircraft, means including a gyroscopefor stabilizing said directional antenna means with respect toorientation of said aircraft about transverse or longitudinal axes, acathode-ray tube, and means including said directional antenna means andsaid cathode-ray tube for indicating the relative locations of saidradiators on a screen of said tube in positions with respect to apredetermined reference line on said screen above or below saidreference line in accordance with whether said aircraft is respectivelybelow or above a glide path at a predetermined elevational angleextending from said landing strip, said means being effectiveirrespective of. the orientation of said aircraft about longitudinal ortransverse axes. SEDGWICK N. WIGHT. OSCAR S. FIEID.

REFERENCES CITED UNITED STATES PATENTS Number Name Date- 1,525,783Trenor Feb. 10, 1925 2,130,913 Tolson Sept. 20, 1938 2,151,549 BeckerMar. 21, 1939 2,210,707 George Oct. 1, 1940 2,226,860 Grieg Dec. 31,'1940 2,226,930 Hefeie Dec. 31, 1940 4 2,255,659 Gage Sept. 9, 19412,262,245 Moseley et al. Nov. 11, 1941 2,280,126 Metcalf Apr. 21, 19422,309,622 Toulon Feb. 13, 1945 2,400,232 Hall May 14, 1946 2,405,231Newhouse Aug. 8, 1948 2,407,275 Hays, Jr Sept. 10, 1946 FOREIGN PATENTSNumber Country Date Great Britain Mar.. 5, 1942

